Preparation process for polypropylene-base resin compositions

ABSTRACT

Disclosed herein is a preparation process for polypropylene-base resin compositions, which process comprises heating at a temperature of 170°-280° C. a mixture containing a crystalline ethylenepropylene block copolymer having a specific composition, an ethylene-propylene copolymer rubber having a specific composition and viscosity, an inorganic filler having a specific particle size, and an organic peroxide, all in specified amounts. The thus-obtained polypropylene-base resin compositions are suitable for use in the production of large moldings such as automobile bumpers, fenders and body sidemembers because of their excellent low-temperature impact resistance, high molding fluidity, good paintability and high stiffness as well as their low preparation cost.

DESCRIPTION

1. Technical Field

This invention relates to a process for preparing polypropylene-baseresin compositions having excellent low-temperature impact resistance,high molding fluidity, superb paintability and high stiffness.

2. Background Art

Although polypropylene resins have heretofore been used widely invarious fields because of their excellent physical properties such aslow specific gravity, high stiffness, and superb chemical and heatresistance, they are accompanied by a drawback in that they have poorimpact resistance at low temperatures. With a view toward overcomingthis drawback, it has been practiced to subject propylene tocopolymerization with ethylene or to blend a rubber-like substance suchas an ethylene-propylene copolymer or polyethylene with polypropylene.In addition, it is also commonly practiced to improve their stiffness,heat resistance, dimensional stability, paintability and the like byincorporating a variety of fillers in polypropylene resins.

Given these conditions, it is, however, required for polypropyleneresins to fulfill such mutually contradictory properties as highstiffness, high heat resistance, easy paintability and high moldingfluidity in combination with high impact resistance. Moreover, each ofthe above properties is required at a high level.

A variety of improvements have been proposed for the above requirementsto date. Most of these proposals are, however, insufficient to meet andbalance the high degrees of physical properties required. Therefore, itmay be required in many instances to add a rubber component, fillers andso on at higher concentrations to polypropylene resins, resulting inincreased costs.

DISCLOSURE OF THE INVENTION

An object of this invention is to provide a preparation process forinexpensive polypropylene-base resin compositions having excellentlow-temperature impact resistance, high molding fluidity and highstiffness.

Another object of this invention is to provide a preparation process forpolypropylene-base resin compositions suitable for use in the productionof large moldings such as automobile bumpers, fenders and bodysidemembers.

The present invention thus provides the following preparation processfor polypropylene-base resin compositions:

A process for preparing polypropylene-base resin compositions, whichprocess comprises heating at a temperature of 170° C.-280° C. a mixturecontaining:

(a) a crystalline ethylene-propylene block copolymer having an ethylenecontent of 7-30 wt. % and having a portion of 65 wt. % or more insolublein boiling n-heptane;

(b) an ethylene-propylene copolymer rubber having a propylene content of40-65 wt. % and a Mooney viscosity of 15-80 at 100° C.;

(c) an inorganic filler having particle sizes of 6 μm or smaller; and

(d) an organic peroxide, said components (a), (b), (c) and (d) beingcontained in amounts of 65-95 wt. %, 35-5 wt. %, 2-25 wt. % and0.001-0.5 wt. %, respectively, all based on the total amount ofcomponents (a) and (b).

BEST MODE FOR CARRYING OUT THE INVENTION

The crystalline ethylene-propylene block copolymer useful in thepractice of this invention has an ethylene content of 7-30 wt. % andhaving a portion of 65 wt. % or more insoluble in boiling n-heptane. Ifthe above ethylene content is less than 7 wt. %, the paintability andimpact resistance of the resulting molding is reduced. On the otherhand, any ethylene content greater than 30 wt. % reduces the modulus offlexural elasticity of the resulting molding. Thus, it is preferable notto use the crystalline ethylene-propylene block copolymer in any amountsoutside the above range.

The ethylene-propylene copolymer rubber, which is also useful in thepractice of this invention, is limited to those having propylenecontents of 40-65 wt. % and Mooney viscosities of 15-80 at 100° C. Ifthe propylene content is less than 40 wt. % in the aboveethylene-propylene copolymer rubber, the resulting molding has poorappearance and reduced low-temperature impact resistance. On the otherhand, any propylene content in excess of 65 wt. % leads to moldingshaving lowered moduli of flexural elasticity and poor paintability.Accordingly, it is preferable not to incorporate the ethylene-propylenecopolymer rubber in any amounts outside the above-defined range. If anethylene-propylene copolymer rubber having a Mooney viscosity smallerthan 15 or greater than 80 is added to the above crystallineethylene-propylene block copolymer, the particle sizes of thethus-dispersed ethylene-propylene copolymer rubber become excessivelysmall or large and the physical properties of the resulting moldingsbecome imbalanced. Hence, it is preferable not to use ethylene-propylenecopolymer rubbers having Mooney viscosities outside the above-definedrange.

In the present invention, the ethylene-propylene copolymer rubber isincorporated in an amount of 5-35 parts by weight per 100 parts byweight of the total amount of the crystalline ethylene-propylene blockcopolymer and the ethylene-propylene copolymer rubber. Any amounts lowerthan 5 parts by weight reduces impact resistance and paintability of theresulting moldings. If the amount of the ethylene-propylene copolymerrubber exceeds 35 parts by weight, the molding fluidity of the resultingcomposition is lowered and the modulus of flexural elasticity of theresulting molding is reduced. Therefore, it is preferable not toincorporate the ethylene-propylene copolymer rubber in any amountsoutside the above-defined range.

As illustrative inorganic fillers useful in the practice of thisinvention, may be mentioned calcium oxide, magnesium oxide, calciumhydroxide, magnesium hydroxide, aluminum hydroxide, magnesium carbonate,calcium carbonate, barium sulfate, talc, clay, glass powder, dolomite,pirssonite, or the like, each having a particle size of 6 μm or smalleror, preferably, 5 μm or smaller. Use of calcium carbonate, bariumsulfate or talc is particularly preferable. These inorganic fillers maybe used either singly or in combination.

If one or more of the above inorganic fillers, the particle sizes ofwhich exceed 6 μm, is used, the impact resistance of the resultingpolypropylene-base resin composition is lowered.

As methods commonly employed for the determination of particle sizes ofinorganic fillers, there are various definitions such as Green's orFeret's particle size, Goebelein's particle size, Nussenstein's particlesize and Stokes's particle size. Particle sizes may be measured inaccordance with a variety of measurement methods as given in the"Chemical Industry Handbook".

The term "particle size" as used herein means Nussenstein's particlesize which is determined by the photo-extinction method. Measurement ofparticle size may be carried out by using, for example, aphoto-extinction particle size distribution analyzer Model SKC-2000(manufactured by Seishin Kigyo Company). As particle size, thatcorresponding to 50% of the cumulative particle size distribution(generally called "D₅₀ ") may be used.

The proportion of the inorganic filler having a particle size of 6 μm orsmaller to be added in the present invention may range from 2-25 partsby weight based on 100 parts by weight of the total amount of the resincomponents consisting of the crystalline ethylene-propylene blockcopolymer and the ethylene-propylene copolymer rubber. Any proportionssmaller than 2 parts by weight are too small to improve stiffness.Stiffness may be further improved to a certain degree as the proportionof the inorganic filler increases beyond 25 parts by weight. However,the incorporation of the inorganic filler in any amounts greater than 25parts by weight lowers paintability. Because of the hygroscopicity ofthe incorporated inorganic filler, in particular, swelling may developbetween the resin layer and the coating layer, resulting in poorresistance to warm water and moisture. Therefore, it is preferable notto add the inorganic filler in any amounts outside the above-definedrange.

Examples of organic peroxides useful in the practice of this inventioninclude t-butyl peroxypivalate, lauroyl peroxide, benzoyl peroxide,cyclohexanone peroxide, t-butyl peroxyisopropylcarbonate, t-butylperoxybenzoate, methyl ethyl ketone peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(6-butylperoxy)hexane, di-t-butyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, or the like. These organicperoxides may be used either singly or in combination.

The proportion of the organic peroxide may range from 0.001 to 0.5 partby weight or, preferably, from 0.01 to 0.3 part by weight based on 100parts by weight of the total amount of the crystallineethylene-propylene block copolymer and the ethylene-propylene copolymerrubber. Any amounts smaller than 0.001 part by weight result in resincompositions having small melt flow indexes and hence poor moldingfluidity. If the amount of the organic peroxide exceeds 0.5 part byweight, on the other hand, the molecular weight of the resin componentof the resulting resin composition of this invention becomes too smallto render the resin composition suitable for practical applications.

It is also possible to add, either singly or in combination,antioxidants, heat stabilizers, ultraviolet absorbents, fire retardants,nucleating agents, organic or inorganic pigments and the like which areroutinely employed in polypropylene resins, so long as their amounts arelimited to the extent that they do not impair the advantages of thepresent invention.

The mixing of the components (a)-(d) in this invention may be carriedout using a Henschel mixer or the like commonly employed in the art.Although the heating of the resulting mixture may be effected by meansof a Banbury mixer, a warming-up mill, or the like, it is generallydesirable to knead the resulting mixture in a molten state and then toform it into pellets by means of a single-screw extruder or adouble-screw extruder. In this case, the temperature of the extruder mayvary depending on the types and amounts of the crystallineethylene-propylene block copolymer and the organic peroxide to be used.It is, however, necessary to control it within 170°-280° C. Anytemperatures lower than 170° C. are too low to achieve thermaldegradation to any sufficient degree, thereby failing to bring about theadvantages of this invention to any significant extent. Even if heatprocessing is carried out at a temperature higher than 280° C., nosignificant increase can be observed with respect to the thermaldegradation effect. It is undesirable to raise the temperature of theextruder to an excessively high level, because such a high temperaturecauses the resin composition to undergo thermal decomposition.

The thus-obtained resin composition may be formed into desired moldingsin accordance with commonly-employed molding methods, for example, bythe injection molding method, the extrusion molding method, thecompression molding method, and the like.

The invention will next be described more specifically in the followingExamples and Comparative Examples, in which melt flow indexes, moduli offlexural elasticity and Izod impact strengths were measured inaccordance with ASTM D-1238, ASTM D-790 and ASTM D-256, respectively:

EXAMPLE 1

Mixed in a Henschel mixer were 80 parts by weight of a crystallineethylene-propylene block copolymer (hereinafter called "PP-A") having anethylene content of 8.5 wt. % and having a portion of 92.0 wt. %insoluble in boiling n-heptane and a melt flow index of 1.3, 20 parts byweight of an ethylene-propylene copolymer rubber having a propylenecontent of 50 wt. % and a Mooney viscosity of 24 at 100° C. (hereinafterreferred to as "EPR-A"), talc having a particle size of 1.3 μm in anamount of 5 parts by weight based on 100 parts by weight of the totalamount of the crystalline ethylene-propylene block copolymer and theethylene-propylene copolymer rubber,2,5-dimethyl-2,5-di(t-butylperoxy)hexane in an amount of 0.13 part byweight based on 100 parts by weight of the total amount of thecrystalline ethylene-propylene block copolymer and theethylene-propylene copolymer rubber, and small amounts of a thermalstabilizer and antioxidant. The resulting mixture was pelletized at 210°C. through an extruder. The thus-obtained pellets were formed intoprescribed specimens using an injection-molding machine, followed bymeasurement of the physical properties of the specimens. Theirpaintability was evaluated in accordance with the following method:

A two-liquid type priming paint of an acrylic component-chlorinatedpolypropylene system was coated to a film thickness of 10 μm over eachof the specimens obtained using the above injection-molding machine.Thereafter, a two-liquid type top-coating paint of an acryliccomponent-urethane system was applied to a thickness of 25 μm over theprimed specimens. After drying the thus-primed and top-coated specimensat 90° C. and for 30 minutes, they were allowed to stand at roomtemperature for 24 hours, thereby obtaining specimens useful in apaintability test. Using a cutter, a grid pattern of 100 1-mm squareswas cut through the coating of each specimen. After applying adhesivetape over the cross-hatched areas, the tape was quickly pulled off. Theratio of remaining squares of the coating was determined in terms ofpercentage, on which the initial adherence was evaluated (thegrid-patterned pulling-off test). In addition, specimens useful in thepaintability test were immersed for 240 hours in warm water of 40° C.and their warm water resistance was then evaluated by observing thestate of the surfaces of the coatings and subjecting them to thegrid-patterned pulling-off test.

Further, after allowing the above-obtained pellets to stand for one weekin an atmosphere of 30° C. and 90% R.H., they were formed into plates160 mm long, 80 mm wide and 2 mm thick by means of an injection-moldingmachine. Surfaces of the resulting moldings were observed. The melt flowindexes of the thus-obtained polypropylene resins, moduli of flexuralelasticity and Izod impact strengths measured on the specimens,evaluation results of the paintability of the specimens and surfaceconditions of the moldings are all given in Table 1.

EXAMPLES 2 and 3

The procedures of Example 1 were repeated escept that talc was added inamounts of 2 parts by weight and 10 parts by weight, respectively, forExamples 2 and 3. Test results are given in Table 1.

COMPARATIVE EXAMPLE 1

The procedures of Example 1 were followed except for the omission oftalc. Test results are given also in Table 1.

COMPARATIVE EXAMPLE 2

The procedures of Example 1 were followed except that talc was added inan amount of 30 parts by weight. Test results are shown in Table 1.

COMPARATIVE EXAMPLE 3

The procedures of Example 1 were repeated except that talc having aparticle size of 7.0 μm was used in lieu of talc having a particle sizeof 1.3 μm. Test results are shown in Table 1.

EXAMPLES 4 and 5

The procedures of Example 1 were repeated except that barium sulfatehaving a particle size of 1.2 μm and calcium carbonate having a particlesize of 1.9 μm, respectively, for Examples 4 and 5, were used asinorganic fillers in place of talc having a particle size of 1.3 μm.Test results are given also in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                   Comp.               Comp.                                                                              Comp.                                                Ex. 1                                                                              Ex. 1                                                                              Ex. 2                                                                              Ex. 3                                                                              Ex. 2                                                                              Ex. 3                                                                              Ex. 4                                                                              Ex. 5                       __________________________________________________________________________    Composition                                                                   (parts by weight)                                                             PP-A           80   80   80   80   80   80   80   80                          EPR-A          20   20   20   20   20   20   20   20                          Talc (1.3 μm)                                                                              0    5    2   10   30   --   --   --                          Talc (7.0 μm)                                                                             --   --   --   --   --    5   --   --                          Barium sulfate (1.2 μm)                                                                   --   --   --   --   --   --    5   --                          Calcium carbonate (1.9 μm)                                                                --   --   --   --   --   --   --    5                          Organic peroxide                                                                             0.13  0.13                                                                              0.13  0.13                                                                               0.13                                                                               0.13                                                                               0.13                                                                               0.13                       Measurement results of                                                        physical properties                                                           Melt flow index (g/10 min.)                                                                  9.6  9.0  9.1  9.0  8.2  9.1  9.5  9.3                         Modulus of flexural elasticity                                                               6800 10500                                                                              8500 11400                                                                              18300                                                                              8900 9000 9500                        (Kg/cm.sup.2)                                                                 Izod                                                                             -40° C.                                                                     (Kg · cm/cm)                                                                not  20.5 not  19.1 7.8  5.5  32.5 19.8                           notched     broken    broken                                               Paintability                                                                         Initial 100/100                                                                            100/000                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                     (1/100)                                                                              Warm water                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                             68/100                                                                             95/100                                                                            100/100                                                                            100/100                            resistance                                                             Appearance*    ○                                                                           ○                                                                           ○                                                                           ○                                                                           X    X    ○                                                                           ○                    __________________________________________________________________________     * ○  : Good; X: Poor                                              

EXAMPLE 6

The procedures of Example 1 were followed except that, in place ofEPR-A, an ethylene-propylene copolymer rubber having a propylene contentof 55 wt. % and a Mooney viscosity of 47 at 100° C. (hereinafterreferred to as "EPR-B") was used. Test results are shown in Table 2.

EXAMPLE 7

The procedures of Example 1 were repeated except that EPR-A was replacedby an ethylene-propylene copolymer rubber having a propylene content of53 wt. % and a Mooney viscosity of 72 at 100° C. (hereinafter referredto as "EPR-C"). Test results are shown in Table 2.

COMPARATIVE EXAMPLE 4

The procedures of Example 1 were followed except that, in place ofEPR-A, an ethylene-propylene copolymer rubber having a propylene contentof 27 wt. % and a Mooney viscosity of 70° at 100° C. (hereinafterreferred to as "EPR-D") was employed. Test results are given in Table 2.

EXAMPLE 8

The procedures of Example 1 were repeated except that PP-A and EPR-Awere added in amounts of 70 parts by weight and 30 parts by weight,respectively. Test results are shown in Table 2.

COMPARATIVE EXAMPLE 5

The procedures of Example 1 were repeated except that PP-A and EPR-Awere added in amounts of 50 parts by weight and 50 parts by weight,respectively. Test results are shown in Table 2.

EXAMPLE 9

The procedures of Example 1 were followed except that a crystallineethylene-propylene block copolymer having an ethylene content of 7.8 wt.% and having a portion of 93.5 wt. % insoluble in boiling heptane and amelt flow index of 3.5 (hereinafter referred to as "PP-B") was usedinstead of PP-A and that the organic peroxide was added in an amount of0.03 part by weight. Test results are shown in Table 2.

COMPARATIVE EXAMPLE 6

The procedures of Example 1 were repeated except for the omission of theorganic peroxide. Test results are shown in Table 2.

COMPARATIVE EXAMPLE 7

The procedures of Example 1 were repeated except that the organicperoxide was added in an amount of 0.6 part by weight. Test results areshown in Table 2.

COMPARATIVE EXAMPLE 8

From the PP-A, EPR-A, talc, organic peroxide, thermal stabilizer andantioxidant used in Example 1, the PP-A, EPR-A, organic peroxide,thermal stabilizer and antioxidant were pelletized in the same manner asin Example 1. Talc was then added to the resultant pellets, followed bypelletization of the resulting mixture in a similar manner. Thethus-obtained pellets were formed into specimens by an injection-moldingmachine. It was observed that talc was poorly distributed in theresultant specimens. This problem was particularly remarkable in planarspecimens. Accordingly, their physical property measurement andpaintability test were omitted.

                                      TABLE 2                                     __________________________________________________________________________                             Comp.     Comp.     Comp.                                                                              Comp.                                      Ex. 6                                                                              Ex. 7                                                                              Ex. 4                                                                              Ex. 8                                                                              Ex. 5                                                                              Ex. 9                                                                              Ex. 6                                                                              Ex. 7                       __________________________________________________________________________    Composition                                                                   (parts by weight)                                                             PP-A           80   80   80   70   50   --   80   80                          PP-B           --   --   --   --   --   80   --   --                          EPR-A          --   --   --   30   50   20   20   20                          EPR-B          20   --   --   --   --   --   --   --                          EPR-C          --   20   --   --   --   --   --   --                          EPR-D          --   --   20   --   --   --   --   --                          Talc (1.3 μm)                                                                              5    5    5    5    5    5    5    5                          Organic peroxide                                                                              0.13                                                                               0.13                                                                               0.13                                                                               0.13                                                                               0.13                                                                               0.03                                                                               0   0.6                         Measurement results of                                                        physical properties                                                           Melt flow index (g/10 min.)                                                                  8.8  8.5  9.5  9.4  6.5  9.6  1.5  8.5                         Modulus of flexural elasticity                                                               10300                                                                              10200                                                                              9500 8800 4700 8900 13800                                                                              9200                        Izod                                                                             -40° C.                                                                     (Kg · cm/cm)                                                                20.7 25.0 6.5  not  not  19.8 27.5 3.8                            notched                    broken                                                                             broken                                     Paintability                                                                         Initial 100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                     (1/100)                                                                              Warm water                                                                            100/100                                                                            100/100                                                                             98/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                                                                            100/100                            resistance                                                             Appearance*    ○                                                                           ○                                                                           X    ○                                                                           ○                                                                           ○                                                                           X    ○                    __________________________________________________________________________     * ○ : Good; X: Poor                                               

We claim:
 1. A process for preparing polypropylene-base resincompositions exhibiting a melt flow index value of at least 8.5 g/10min., a modulus of flexural elasticity of at least 8500 kg/cm² and anIzod value, notched at -40° C., of at least 19.1 Kg.cm/cm, which processcomprises heating at a temperature of 170° C.-280° C. a mixturecontaining:(a) a crystalline ethylene-propylene block copolymer havingan ethylene content of 7-30 wt. % and having a portion of 65 wt. % ormore insoluble in boiling n-heptane; (b) an ethylene-propylene copolymerrubber having a propylene content of 40-65 wt. % and a Mooney viscosityof 15-80 at 100° C.; (c) and inorganic filler having a particle size of6 μm or smaller; and (d) an organic peroxide, said components (a), (b),(c) and (d) being contained in amounts of 65-95 wt. %, 35-5 wt. %, 2-25wt. % and 0.001-0.5 wt. %, respectively, all based on the total amountof components (a) and (b).
 2. A method according to claim 1, wherein theinorganic filler has a particle size of 5 μm or smaller.
 3. A methodaccording to claim 1, wherein the inorganic filler is selected fromcalcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide,aluminum hydroxide, magnesium carbonate, calcium carbonate, bariumsulfate, talc, clay, glass powder, dolomite or pirssonite.
 4. A methodaccording to claim 1, wherein the inorganic filler is selected fromcalcium carbonate, barium sulfate or talc.
 5. A method according toclaim 1, wherein the organic peroxide is selected from t-butylperoxypivalate, lauroyl peroxide, benzoyl peroxide, cyclohexanoneperoxide, t-butyl peroxyisopropyl-carbonate, t-butyl peroxybenzoate,methyl ethyl ketone peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide or2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
 6. A method according toclaim 1, wherein the components (a), (b), (c) and (d) are mixed and thenheated to a temperature of 170°-280° C. for thermal degradation.
 7. Amethod according to claim 1, wherein the components (a), (b), (c) and(d) are kneaded in a molten state at a temperature of 170°-280° C. andthen pelletized for thermal degradation.